Study on isolation of protease-producing microbes and production of high-quality protein stuffs by solid-state fermentation

Abstract

Protein resources are severely short around the world, especially for the requirement of animal production. How to solve this problem has become more and more important. The production of high-quality protein stuffs from the low-quality unconventional protein resources by microbial fermentation is the main research direction all over the world. In this study, the low-quality protein stuffs such as cottonseed, blood and feather meals were fermented by Aspergillus oryzae (A. oryzae), which was isolated from bovine rumen and identified by 26S rDNA. The orthogonal experiment and single factor analysis of variance method was used to select the optimal fermentation nutrient media and conditions. The results showed that the optimum medium compositions of raw materials for replacing soybean meal were 30% blood meal, 26% cottonseed meal, 4% feather meal, 35% wheat bran, 5% corn flour; the best fermentation conditions were initial pH 6, 40% moisture, 2% fungal inoculation volume, and 60 h fermentation. Under the best conditions of solid-state fermentation (SSF), the soluble protein content, amino nitrogen content, crude protein content, free amino acids in the fermented products were 173.72 mg/g, 34.75 mg/g, 48.97%, 100.95 mg/g, which were increased by 82.68%, 379.97%, 12.91%, 570.00%, compared with the unfermented product, respectively (P<0.05). The activities of protease, amylase and cellulase in the fermented products were 2341.83 U/g, 36780.8 U/g and 6835.43 U/g, respectively. It can be concluded that the unconventional protein resources can be significantly improved by using the method of SSF of A. oryzae. The experiment result will provide an important theoretical basis for solving current shortage of protein feed resources.